JPH08259376A - Production of oxide single crystal and apparatus therefor - Google Patents

Abstract

PURPOSE: To continuously obtain, through e.g. μ pull-down process, a high-quality oxide single crystal in a comparatively large quantities by treating a large quantity of a stock so as to prevent the variation, etc., in the composition of the final product. CONSTITUTION: A stock is fed into a crucible 7 and melted, a seed crystal is then brought into contact with the resultant melt 8, which is then pulled down from the crucible 7, thus growing the objective oxide single crystal 14. The single crystal 14 being formed continuously is irradiated with laser beams R and the output beams S from the single crystal 14 is measured, and based on the measurements, the composition ratio for the stock to be fed from a stock feeder 24 is controlled.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an oxide single crystal and an apparatus therefor.

[0002]

2. Description of the Related Art Recently, as a method for growing an oxide single crystal, a method of forming a single crystal fiber by a so-called μ pulling down method has been attracting attention. "Electronic Research Institute News" 1
In July 993 (522), pages 4-8, this method is used to describe potassium niobate / potassium / lithium (K ₃ Li _2-2x
Nb _{5 + x} O _{15 + x} , hereinafter referred to as KLN. ) The history of growing single crystal fibers is disclosed.

According to this method, electric power is supplied to a platinum cell or crucible for resistance heating. A melt outlet is formed at the bottom of this cell, and a rod-shaped body called a melt feeder is inserted into this outlet, whereby the amount of melt supplied to the outlet and the solid phase Both control the state of the interface. By adjusting the diameter of the melt outlet, the thickness of the feeder, the length of protrusion of the feeder from the outlet, etc., a thin KLN single crystal fiber is continuously formed. According to this μ pulling down method, the diameter is 1 mm
The following single crystal fibers can be formed, thermal strain can be reduced, convection in the melt can be easily controlled, and the diameter of the single crystal fiber can be easily controlled. It has the feature that high quality single crystals can be produced.

[0004]

DISCLOSURE OF THE INVENTION The present inventor has
We have been conducting research to mass produce KLN single crystal fibers and the like by the pull-down method. The most important mass production technique is to increase the size of the crucible to process a large amount of melt, and to pull the single crystal fiber from the crucible continuously for a long time. Therefore,
The present inventor increased the amount of powder to be added to the crucible up to about 5 g, increased the size of the crucible accordingly, supplied electric power to the crucible to generate heat, and melted the raw material powder in the crucible, I tried the micro pull-down method.

However, it has been found that it is extremely difficult to pull down the melt from the outlet to form a single crystal when the size of the crucible is increased and the melting amount of the powder is increased. Specifically, when the temperature of the furnace in which the crucible is installed is set to 900 ° C. or lower and the powder in the crucible is melted mainly by energizing the crucible, the crystal growth in the vicinity of the draw-out port can be performed well. I didn't understand. That is, when the power supplied to the crucible was increased, the melt melted at the outlet and was not crystallized, and when this power was decreased, the melt became solid near the outlet and the melt could not be withdrawn.

When the temperature of the above-mentioned furnace is raised above 900 ° C., the whole crucible is heated to a large extent due to the radiant heat from the furnace, and the temperature gradient in the vicinity of the outlet becomes very small. It was not possible to grow crystals continuously.

The inventor of the present invention, in order to solve this problem,
We have developed a method to continuously pull out single crystal fibers.
This method will be described later. However, especially from the viewpoint of continuously pulling out single crystal fibers and mass-producing,
Further problems have turned out to remain.

That is, it is necessary to prevent fluctuations in the quality of single crystal fibers, especially in composition. In particular, when producing materials for elements for second harmonics and solid-state lasers, even if the composition changes slightly, the characteristics will change significantly, resulting in defective products. It is necessary to prevent the composition from fluctuating when continuously drawing out.

In the conventional μ-pulling-down method, a single crystal fiber simply pulled out from the outlet of the crucible,
Its composition was measured. In this way, if the method of measuring the composition after cutting out the single crystal fiber is adopted, the composition of the produced material can be surely known. However, since the growth process of single crystal fiber by the μ-pulling down method is a complicated delicate chemical and rheological system in which a large number of factors are correlated, in such a manufacturing system, it responds to a slight change in condition. As a result, the composition of the single crystal fiber often shifts. As a result, all of the large number of single crystal fibers may become defective products, and therefore measures for improving the yield are indispensable.

An object of the present invention is to detect the composition change of an oxide single crystal in real time by detecting the composition change of the oxide single crystal in real time when the oxide single crystal is continuously lowered by the μ-pulling down method. Is to prevent fluctuations in the yield and dramatically improve the yield.

[0011]

According to the method of the present invention, a raw material for an oxide single crystal is supplied into a crucible and melted, and a seed crystal is brought into contact with the melt to form an oxide single crystal. When growing, the oxide single crystal is irradiated with laser light, the output light from the oxide single crystal is measured, and the composition ratio of the raw material supplied to the crucible is controlled according to this measurement value. And

Further, according to the present invention, a raw material of an oxide single crystal is supplied into a crucible and melted, and a seed crystal is brought into contact with the melt to grow the oxide single crystal. A raw material supply device for supplying a raw material to the crucible; a drive device for pulling out the oxide single crystal from the crucible; a laser light source for irradiating the oxide single crystal with laser light; And a controller for controlling the composition ratio of the raw material supplied to the crucible according to the output from the measuring device; The present invention relates to an apparatus for producing a single crystal of a substance.

[0013]

The present inventor has succeeded in solving the above-mentioned problems and continuously pulling down the single crystal fiber and keeping its composition constant. Specifically, a supply device that supplies the raw material of the oxide single crystal to the crucible is provided, and the oxide single crystal that is pulled down is irradiated with laser light to obtain the oxide single crystal. It was found that by measuring the output light from the, and by controlling the composition ratio of the raw material supplied to the crucible according to this measurement value, it is possible to prevent the fluctuation of the composition even if the single crystal fiber or the like is continuously drawn. .

More specifically, when the peak wavelength of the output light of the oxide single crystal shifts to the long wavelength side or the short wavelength side,
Since it means that the composition of the single crystal is deviated, the composition ratio of the raw material is changed so as to reduce the shift of the peak wavelength. This makes it possible to hold the composition within a certain range while pulling out the single crystal fiber or the like.

[0015]

EXAMPLE A laser beam was applied to an oxide single crystal having a second harmonic generation effect, and 2
It is even more preferable to detect overtones. As such an oxide single crystal, it is possible to apply to a known oxide single crystal, but especially KLN, KLTN, KN, SH,
An oxide single crystal that emits blue light by G, CLBO,
Oxide single crystals that generate further ultraviolet light, such as BBO and LBO, are preferable. Of course, it goes without saying that the present invention can be applied to wavelength conversion of higher order such as the third harmonic and the fourth harmonic.

Further, if the laser light for irradiating the oxide single crystal has a wavelength range including a wavelength corresponding to a desired composition, the output light from the oxide single crystal is analyzed by a spectrum analyzer. The intensity can be known for each wavelength within a predetermined wavelength range by detecting with.

Specifically, in FIG. 1, it is assumed that the wavelength of the output light corresponding to the desired composition is λ ₀ and the laser light contains light between the wavelengths λ ₁ and λ _2. . The intensity of the laser light between wavelengths λ ₁ and ₂ is detected with a spectrum analyzer. When the composition of the oxide single crystal pulled down from the extraction port of the crucible is the target composition, the intensity of the laser light has the maximum value T at the wavelength λ ₀ .
However, as manufacturing progresses, the thermal state near the outlet of the oxide single crystal, the influence of gravity, etc. change subtly, and this peak wavelength tends toward λ ₁ or λ _2. Move slightly. Along with this, the graph H also slightly moves in the direction of the arrow F or the direction of the arrow G.

Therefore, when the composition of the oxide single crystal is changed at the stage of pulling down the oxide single crystal and the peak wavelength of the output light is changed, the change of the peak wavelength is immediately detected and the raw material is supplied to the raw material supply device. You can give feedback.

Further, when the light receiving device cannot detect the distribution of the wavelength component like the photodiode, the intensity of the output light of each wavelength cannot be directly known. Therefore, a preferable monitoring method in this case will be described with reference to FIG.

Let λ ₀ be the wavelength of the output light corresponding to the desired composition. When the composition of the oxide single crystal pulled down from the extraction port of the crucible is the target composition, the intensity of the laser light has the maximum value T at the wavelength λ ₀ . As manufacturing progresses, the peak wavelength λ ₀ slightly shifts to λ ₄ or λ ₅ , as described above. Along with this, the graph H moves toward the right side or the left side, and the graph I
Or graph J is obtained.

However, the shift of this maximum value is small,
Moreover, the shape of the whole graph is usually extremely small around the maximum value. Therefore, it has been found that it is practically difficult to detect a change in composition because the change in output at the wavelength λ ₀ is much smaller when the maximum value of the graph is slightly moved.

Therefore, a wavelength 2λ larger than the wavelength 2λ _0
The oxide single crystal is irradiated with a first laser beam having a wavelength of ₇ and a second laser beam having a wavelength of 2λ ₆ which is smaller than the wavelength of 2λ _0. A light receiving device for measuring the intensity of output light was provided. Then, the intensities of the output light corresponding to the first laser light and the output light corresponding to the second laser light were detected.

As a result, when the composition of the oxide single crystal pulled down from the crucible outlet is the desired composition, the intensity at wavelength λ ₆ is p ₀ and the intensity at wavelength λ ₇ is q ₀ . Become. As manufacturing progresses, the peak wavelength λ ₀
Moves toward λ ₅ , graph H moves to the right and becomes graph I. At this time, the wavelength λ
The intensity at ₆ is p ₁ , which is smaller than p ₀ . On the other hand, the intensity at the wavelength λ ₇ is q ₁ , which is larger than q ₀ . On the other hand, when the peak wavelength λ ₀ moves toward λ ₄ , the graph H moves toward the left,
It becomes graph J. At this time, the intensity at the wavelength λ ₆ becomes p ₂ , which is larger than p ₀ . On the other hand, the intensity at the wavelength λ ₇ is q ₂ , which is smaller than q ₀ .

Thus, there is an increase and decrease at both wavelengths.
It appears as a pair, so it is extremely resistant to composition changes
Sensitivity is improved. Moreover, especially the peak wavelength λ ₀, Λ
_Four, Λ_FiveAvoid measuring the vicinity and select the measurement wavelength outside it.
By using the relatively large slope of the graph
Therefore, the sensitivity is better from this viewpoint as well.
become.

In the above method, the first laser light and the second laser light can be simultaneously irradiated,
It is also possible to irradiate each laser beam of two different wavelengths sequentially with a time shift using a wavelength tunable laser.

In the present invention, it is preferable to measure the dimension of the cross section of the oxide single crystal by an optical sensor.
In the single crystal growth, the shape of the cross section is usually controlled to be constant, but the control accuracy can be improved by precisely measuring the dimension and canceling the variation in the light transmission thickness.

Next, preferred embodiments of the present invention will be described in more detail. The inventors of the present invention continued research to increase the size of the crucible in order to establish a mass production technique for the oxide single crystal by the μ-pulling-down method. A single crystal growth part was provided at the lower end of this nozzle part, and the temperature of the crucible and the single crystal growth part were controlled independently of each other.

As a result, the amount of powder melted in the crucible was adjusted to 5
It has been found that the oxide single crystal can be easily and continuously pulled down even if the volume of the crucible is increased to a large amount such as g or more.

The reason why such an effect is obtained is probably that the single crystal growing portion is less likely to be directly affected by the amount of heat generated by the melt in the crucible by providing the single crystal growing portion at the lower end of the nozzle portion. This is probably because it was possible to increase the temperature gradient in the vicinity of the single crystal growing portion by controlling the temperatures of the single crystal growing portion or nozzle portion and the crucible separately at the same time.

Moreover, according to this method, even when the amount of the raw material powder melted in the crucible is increased to about 30 to 50 g, the compositional variation in the KLN single crystal fiber is only 0.01 mol% or less. It was discovered that the accuracy had decreased to a surprising level. Therefore, by combining this manufacturing method with the present invention, it is possible to mass-produce an oxide single crystal having such an extremely highly accurate composition.

Furthermore, the present inventor studied the state of the melt in the single crystal growth part and the physical properties of the single crystal using the above-mentioned manufacturing apparatus. As a result, when the surface tension is more dominant than the gravity in the environment of the single crystal growth part, it is possible to continuously extract a good oxide single crystal with extremely small fluctuation in composition. I found it. This is probably because a good solid-liquid phase interface is formed.

As described above, in order to generate a condition in which the surface tension is more dominant than the gravity in the single crystal growing portion, a mechanism for reducing the gravity applied to the melt in the nozzle portion is provided in the crucible. Is effective. The inventor
Although such a mechanism was examined, particularly by setting the inner diameter of the nozzle portion to be 0.5 mm or less, a condition in which the surface tension is more dominant than the gravity applied to the melt in the nozzle portion can be generated. It was confirmed that a uniform meniscus could be formed at the tip opening of the.

However, the inner diameter of this nozzle is 0.01 m.
If it is less than m, the growth rate of the single crystal becomes too small. Therefore, from the viewpoint of mass production, the inner diameter of the nozzle portion is preferably 0.01 mm or more. The optimum inner diameter of the nozzle is
Within the range of 0.01 to 0.5 mm, it slightly varies depending on the viscosity of the melt, the surface tension, the specific gravity, the growth rate of the single crystal, and the like.

Further, as a result of pursuing this point, the present inventor has obtained the following knowledge. That is, in the conventional μ pulling down method, it is considered that the single crystal fiber could be continuously pulled down because the scale of the crucible was small, but this was because the amount of melt in the crucible was small,
Since the melt adhered to the wall surface of the crucible due to its surface tension, the gravity applied to the outlet was relatively small.Therefore, a solid-liquid phase interface was formed to a certain extent. Can be estimated. However, it is presumed that when the size of the crucible was increased, the condition in which the surface tension was dominant near the outlet was lost.

Further, in this method, it is easy to increase the temperature gradient in the vicinity of the single crystal growing portion when the nozzle portion is viewed in the lengthwise direction. by this,
The melt flowing down in the nozzle part can be cooled rapidly.

Therefore, this manufacturing method is particularly suitable for manufacturing a solid solution single crystal. The solid solution single crystal has a property that the composition ratio varies under equilibrium conditions. When the conventional μ-down method is used, the composition of the solid solution fluctuates due to a slight temperature change or a change in the solidification rate because the equilibrium condition is present near the outlet, which is considered to be due to such a cause. On the other hand, according to the method and apparatus of the present invention, rapid cooling in the vicinity of the single crystal growth portion is possible, and therefore the composition of the melt can be maintained.

As such a solid solution, for example, KL
N, KLTN [K₃Li _2-2x(Ta_yNb_1-y)_{5 + x}]
O_{15 + x}, Ba_1-XSr_XNb₂O₆Tongue
Examples of structure of stainless bronze and Mn-Zn ferrite
Can be

When the raw material is supplied to the crucible, the heat of fusion of the raw material causes a change in the thermal state in the crucible, which causes a change in the composition of the single crystal. However, when the nozzle portion is provided below the crucible as described above, the raw material can be continuously or intermittently supplied to the crucible. This is because even if the above-mentioned thermal fluctuations occur in the crucible, the thermal effect on the single crystal growth part is small, and the single crystal growth part is not in an equilibrium state but in a kinetic state, so thermal fluctuations This is because it is less likely to be affected by.

In the manufacturing apparatus of the present invention, the method of heating the crucible is not particularly limited. However, it is preferable to provide a heating furnace so as to surround the single crystal manufacturing apparatus. At this time, the heating furnace is separated into an upper furnace and a lower furnace, the crucible is surrounded by the upper furnace, and the upper furnace is caused to generate heat at a relatively high temperature, which helps melting the powder in the crucible. preferable. On the other hand, a lower furnace is installed around the nozzle,
By relatively lowering the temperature of the lower furnace, it is preferable to increase the temperature gradient in the single crystal growing portion at the lower end of the nozzle portion.

Further, in order to improve the efficiency of melting the powder in the crucible, rather than heating the crucible only by the heating furnace outside the crucible, the crucible itself is made of a conductive material and the crucible is supplied with electric power. It is preferable to heat the crucible by supplying Further, in order to maintain the molten state of the molten material flowing in the nozzle portion, it is preferable that the nozzle portion is formed of a conductive material and that the nozzle portion is heated to generate heat.

In order to increase the temperature gradient particularly in the single crystal growing portion, it is preferable to separate the energizing mechanism of the crucible and the energizing mechanism of the nozzle part so that they can be independently controlled.

As such a conductive material, from the viewpoint of corrosion resistance, materials such as platinum, platinum-gold alloy, platinum-rhodium alloy, platinum-iridium alloy, and iridium are preferable.

However, since all corrosion-resistant metals such as platinum have a relatively low resistivity, in order to supply electric power to the metal and effectively generate heat, the thickness of the nozzle portion is reduced. It is necessary to increase the resistance value to some extent or more. For example, when the nozzle portion was formed of platinum, it was necessary to form a thin film having a thickness of about 100 to 200 μm. However, when the nozzle portion is formed of such a thin film, the nozzle portion is structurally weakened and the nozzle portion is deformed, which may make stable production of a single crystal difficult.

Therefore, the resistance heating material is installed so as to surround the nozzle portion, and electric power is supplied to the resistance heating material, so that the resistance heating material can generate heat. In this case, the nozzle portion may be formed of the corrosion-resistant metal as described above, and current may be supplied to generate heat, but power may not be supplied. In this way, if the resistance heating material that surrounds the nozzle portion is given a major heating function, the heat load required for the nozzle portion is reduced, and it is not necessary to heat the nozzle portion. By making the part thicker (for example, 300 μm or more), the mechanical strength of the nozzle part can be improved, and the device suitable for mass production can be obtained.

The present invention can be favorably applied not only to the production of single crystal fibers, but also to the production of plate-like bodies or plates made of single crystals. A specific plate forming method will be described later.

The KLN single crystal has recently attracted attention as an optical material, particularly as a single crystal for a blue light second harmonic generation (SHG) element for a semiconductor laser. Since it is possible to generate up to the ultraviolet light region of 390 nm, by using such short wavelength light, it is possible to have a wide range of applications such as optical disk memory, medical, photochemical, and various optical measurement. is there. Further, since the KLN single crystal also has a large electro-optical effect, it can be applied to an optical storage element or the like utilizing the photorefractive effect.

FIG. 3 is a schematic sectional view showing a manufacturing apparatus for growing a single crystal according to one embodiment of the present invention.
(B) is a conceptual diagram for explaining the state of the tip portion of the nozzle portion.

A crucible 7 is installed inside the furnace body. To surround the crucible 7 and its upper space 5,
An upper furnace 1 is installed, and a heater 2 is installed in the upper furnace 1.
Is buried. The nozzle portion 13 extends downward from the lower end portion of the crucible 7, and an opening 13 a is formed in the lower end portion of the nozzle portion 13. The lower furnace 3 is installed so as to surround the nozzle portion 13 and the space 6 around the nozzle portion 13, and the heater 4 is embedded in the lower furnace 3.
Of course, the form itself of such a heating furnace can be variously changed. For example, in FIG. 1, the heating furnace is divided into two zones, but the heating furnace may be divided into three zones or more. Both the crucible 7 and the nozzle portion 13 are made of a corrosion-resistant conductive material.

To the position A of the crucible 7, one electrode of the power source 10A is connected by the electric wire 9,
The other electrode of the power supply 10A is connected to the lower bent end B. One electrode of the power supply 10B is connected to the position C of the nozzle portion 13 by the electric wire 9,
The other electrode is connected to the lower end D of the nozzle portion 13. Each of these energization mechanisms is separated together and is configured so that its voltage can be controlled independently.

Further, after heaters 12 are provided in the space 6 at intervals so as to surround the nozzle portion 13. An intake pipe 11 extends upward in the crucible 7, and an intake port 22 is provided at an upper end of the intake pipe 11. The intake 22 slightly projects from the bottom of the melt 8.

The melt intake port may be formed at the bottom of the crucible so as not to project from the bottom of the crucible. In this case, the intake pipe 11 is not provided. However, if this crucible is used for a long period of time, impurities in the melt may gradually accumulate at the bottom of the crucible. As in the present embodiment, by providing the intake port 22 at the upper end of the intake pipe 11, even if impurities are collected at the bottom of the crucible, the intake pipe 11 projects from the bottom, so that the impurities at the bottom are introduced into the intake port. It is hard to enter.

The upper furnace 1, the lower furnace 3 and the after-heater 12 are caused to generate heat to appropriately determine the temperature distribution in the spaces 5 and 6, and the raw material of the melt is supplied into the crucible 7 to the crucible 7 and the nozzle portion 13. Electricity is supplied to generate heat. In this state, as shown in FIG. 4A, in the single crystal growth portion 23 at the lower end of the nozzle portion 13, the melt 8
Slightly protrudes and is held by the surface tension, so that a relatively flat surface 17 is formed.

The gravity applied to the melt 8 in the nozzle portion 13 is greatly reduced by the contact of the melt with the wall surface in the nozzle portion 13. In particular, by setting the inner diameter of the nozzle portion 13 to 0.5 mm or less, it was possible to form a uniform solid-liquid phase interface as described above.

In this state, seed crystal 15 is moved upward as shown by arrow E, and end face 15a of seed crystal 15 is brought into contact with surface 17. Next, as shown in FIG. 4B, the seed crystal 15 is pulled down. At this time, a uniform solid-liquid-phase interface (meniscus) 19 is formed between the upper end of the seed crystal 15 and the melt 8 drawn out downward from the nozzle 13.

As a result, as shown in FIG. 3, the single crystal fiber 14 is continuously formed on the upper side of the seed crystal and is drawn downward. In this embodiment, the single crystal fiber 14 is sent by a roller 28 which is a driving device.

On the other hand, when a conventional crucible is used and the amount of the powder to be added thereto is increased, an expanded portion due to the melt is formed downward from the crucible outlet. If the end face 15a of the seed crystal 15 is brought into contact with the melt in this state, a good solid-liquid phase interface is not formed.

When the single crystal fiber is continuously drawn downward, the laser light source 27 emits a laser beam having a wavelength of about 2λ ₀ as shown by an arrow R and irradiates the single crystal fiber 14 with the laser beam. The output light S near the second harmonic λ ₀ from the single crystal fiber is received by the light receiving device 26 through the long wavelength cut filter 41, and its intensity is detected. The signal from the light receiving device 26 is sent to the control device 33 through the signal line 25, processed there, and the composition ratio of the raw material fed from the raw material supply device 24 on the crucible 7 is controlled.
When the measured value of the intensity of the output light fluctuates from the predetermined target value, the control device 33 sends a signal for changing the composition ratio of the raw material to the raw material supply device 24 to feed it back.

For more accurate control, a part of the long wavelength around 2λ ₀ can be combined with the reflection mirror 29 and the light receiving device 26, and the signal can be sent to the control device 33 through the signal line 25.

Hereinafter, more specific experimental results will be described. (Experiment 1) Using a single crystal manufacturing apparatus as shown in FIG.
KLN single crystal fibers were produced according to the present invention. The temperature inside the furnace was controlled by the upper furnace 1 and the lower furnace 3. The temperature gradient in the vicinity of the single crystal growth part 23 can be controlled by supplying power to the nozzle part 13 and generating heat from the after-heater 12. As a mechanism for pulling down the single crystal fiber, a mechanism for pulling down the single crystal fiber was mounted while controlling the pulling speed uniformly within the range of 2 to 100 mm / hour in the vertical direction. Laser light source 2
As No. 7, a titanium sapphire laser light source, which is a tunable laser capable of modulating the wavelength within a wavelength range of 780 to 900 nm, was used.

Potassium carbonate, lithium carbonate and niobium oxide were mixed in a composition ratio of 30:20:50 to produce a raw material powder. About 50 g of the raw material powder was supplied into the crucible 7 made of platinum, and the crucible 7 was set at a predetermined position.
The temperature of the space 5 in the upper furnace 1 was adjusted to a range of 1100 to 1200 ° C. to melt the raw material in the crucible 7. Lower furnace 3
The temperature of the inner space 6 was uniformly controlled at 500 to 1000 ° C. Predetermined electric power was supplied to the crucible 7, the nozzle portion 13 and the after-heater 12 to grow a single crystal. At this time, the temperature of the single crystal growing portion is set to 1050 ° C to 115 ° C.
The temperature could be set to 0 ° C., and the temperature gradient in the single crystal growing portion could be controlled to 10 to 50 ° C./mm.

The outer and inner cross-sectional shapes of the nozzle portion 13 are circular, the outer diameter is 1 mm, and the inner diameter is 0.1 mm.
And the length was 20 mm. The planar shape of the crucible 7 is circular, its diameter is 30 mm, and its height is 30 mm.
And In this state, the single crystal fiber was pulled down at a speed of 20 mm / hour.

At the same time, a single-crystal fiber was irradiated with laser light in the vicinity of the intended phase matching wavelength (850 nm) from a titanium sapphire laser light source, and the output light was analyzed by a spectrum analyzer. As a raw material,
The following two types of powders were used. Powder 1: K _3.1 Li ₂ Nb ₅ O Powder 2: K _2.9 Li ₂ Nb ₅ O

At the beginning, the powder 1 and the powder 2 are 1: 1.
The mixture was mixed in the ratio of, and put into a crucible. When the peak wavelength fluctuated, the amount of powder 1 was increased, and when the peak wavelength fluctuated, the amount of powder 2 was increased.

In this way, the single crystal fiber having a length of 1 mm, a width of 1 mm and a length of 100 mm was continuously grown and the mixing ratio of the raw material powders was controlled. As a result, the phase matching wavelength of this single crystal has an accuracy of 0.2 nm or less, that is, 0.01 mol% or less in terms of composition.
The composition could be controlled with high accuracy as never before as a KLN single crystal.

(Experiment 2) In the same manner as in Experiment 1, a KLN single crystal fiber was grown. However, a single crystal fiber was continuously grown by providing a cutting device under the furnace for intermittently cutting the single crystal fiber to a predetermined length. As the growth of the single crystal fiber progressed, the raw material powder was supplied into the crucible 7 in an amount corresponding to the amount of the grown single crystal and the amount of the component volatilized from the crucible 7. At this time, the mixing ratio of each powder was determined as described above.

Thus, a single crystal fiber having a length of about 10 m was continuously formed. As a result, the phase matching wavelength of this single crystal was set to 0.
The accuracy can be suppressed to 2 nm or less, that is, the composition variation has been successfully suppressed to 0.01 mol% or less.

(Experiment 3) In the nozzle portion 13 described above, the shape thereof is an elongated plate shape, and the thickness of the KL is 0.3 mm.
Succeeded in pulling down the N single crystal plate.

In this case, the raw material supply was controlled by observing changes in the output light of the two types of semiconductor lasers. As shown in FIG. 5, with respect to the target wavelength λ ₀ (425 nm), 2λ ₆ (848 nm, that is, 424 × 2 nm)
Laser light source 27A for generating laser light of 2λ ₇
A laser light source 27B that generates a laser beam of (852 nm, that is, 426 × 2 nm) is prepared. As shown in FIG. 5, the light receiving devices 26A and 26B corresponding to each of these laser light sources are installed on the opposite sides of the single crystal plate 40.

Due to the variation of the composition of the single crystal, λ ₀ is 42
If there is a fluctuation even from 5 nm to 0.2 nm, the outputs of the light receiving devices 26A and 26B change correspondingly,
The change in the output was sent to the control device 33, and the change in the output was fed back to the mixing ratio of the raw material powder through the control device 33 to control the growth of the single crystal.

Since the phase matching half width of the second harmonic changes depending on the thickness and quality of the crystal, it is necessary to select the wavelength of the laser light source. KLN has a thickness of 0.3 mm,
Theoretically, there is a width of 3.5 nm, so
λ ₆ and 2λ ₇ are selected, but when the thickness is 0.6 mm, 2λ ₆ (849 nm, that is, 424.5 × 2n
m) 2λ ₇ (851 nm, that is, 425.5 × 2n
m) can be used to control.

Needless to say, the mixing ratio of the raw material powder can be feedback-controlled even in the case of a single crystal fiber by such a control method.

(Reference Experiment 1) A KLN single crystal fiber similar to that of Experiment 1 was prepared by using a manufacturing apparatus having a conventional structure. The amount of raw material powder was 500 mg. The crucible was made of platinum. The temperature inside the furnace was controlled by the upper furnace and the lower furnace. Set the temperature of the space in the upper furnace to 1100-1
The raw material in the crucible was melted by adjusting the temperature within the range of 200 ° C. The temperature of the space 6 in the lower furnace 3 is 500 to 1000 ° C.
Controlled uniformly. An electric power was supplied to the crucible, and an attempt was made to control the growth and the pulling out of the single crystal from the pulling opening by this. In this state, when the single crystal fiber was pulled down at a speed of 20 mm / hour, the KLN single crystal fiber could be pulled down.

Thus manufactured, length 1 mm, width 1 mm,
With respect to a single crystal fiber having a length of 100 mm, the composition distribution when the single crystal fiber was viewed in the length direction (growing direction) was examined in the same manner as in Experiment 1. As a result, the wavelength of the output light changed by 50 nm. This exceeds 1.0 mol% in terms of composition, and S
For HG devices, there was a problem in practical use.

(Reference Experiment 2) In Comparative Experiment 1, raw material powders in an amount corresponding to the amounts of the components extracted from the crucible and the components evaporated from the crucible were periodically supplied to the crucible to continuously produce a single crystal. Tried to grow fibers. However, once the raw material was supplied, the thermal equilibrium state in the crucible was greatly disrupted, making it impossible to continue growing the single crystal fiber.

Reference Experiment 3 In Comparative Experiment 1, the size of the crucible was increased and the amount of raw material powder initially charged into the crucible was increased to 5 g. An attempt was made to control the temperature in the entire furnace by the upper furnace and the lower furnace and supply electric power to the crucible, thereby controlling the growth and extraction of the single crystal from the extraction port.

However, the temperature in the upper furnace is set to 500 to 900.
If the temperature is adjusted to a low value of ℃, it is necessary to increase the power supply to the crucible to accelerate the melting of the raw material powder in the crucible. However, when the output was increased, the melt did not crystallize. On the other hand, when the power supplied to the crucible was reduced, the melt solidified before it came out of the outlet. Thus, it was not possible to find the conditions for pulling out the single crystal.

On the other hand, when the temperature of the upper furnace is set to 900 ° C. or higher, the heat radiation from the furnace body makes it impossible to maintain the temperature gradient necessary for crystallization in the vicinity of the drawing port, which is the crystal growth point. The single crystal fiber could not be pulled down.

[0078]

As described above, according to the present invention, μ
When growing an oxide single crystal by the pull-down method,
It is possible to process a large amount of raw materials and continuously pull down a large amount of oxide single crystals to form, and to prevent fluctuations in the composition of these oxide single crystals, etc. to produce high quality oxide single crystals. can do. Therefore, the present invention is a very important technique for mass-producing such oxide single crystal fibers.

[Brief description of drawings]

FIG. 1 is a graph showing a relationship between wavelength and intensity of output light.

FIG. 2 is a graph for explaining a mode of measuring the intensity of output light having a wavelength on both sides of a target wavelength λ ₀ .

FIG. 3 is a schematic sectional view showing a manufacturing apparatus for growing a single crystal according to an embodiment of the present invention.

4 (a) and 4 (b) are conceptual diagrams for explaining a state of a tip portion of a nozzle portion 13 of a manufacturing apparatus for growing a single crystal.

FIG. 5 is a block diagram for explaining a feedback control method using a pair of laser light sources 27A and 27B and light receiving devices 26A and 26B.

[Explanation of symbols]

1 Upper Furnace 2 and 4 Heater in Furnace 3 Lower Furnace 5 Space in Upper Furnace 1 6 Space in Lower Furnace 3
7 Crucible 8 Melt 10A, 10B Power supply (energization mechanism) 11 Intake pipe 12 After heater 13 Nozzle part
14 Single Crystal Fiber or Plate 15 Seed Crystal 19 Interface between Solid Phase and Liquid Phase 22 Melt Intake Port 23 Single Crystal Growth Section 24 Raw Material Supply Device
26 light receiving device 27 laser light source 28 roller 29 reflection mirror for reflecting a part of long wavelength
30 Surface of melt 33 Control device 41 Long wavelength cut filter H, I, J Graph showing relationship between wavelength and intensity of output light R Laser light S Output light λ ₀ Target peak wavelength λ ₄ , λ ₅ Target value Deviated peak wavelength λ ₆ , λ ₇ Measurement wavelength

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[Procedure amendment]

[Submission date] June 20, 1996

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0059

[Correction method] Change

[Correction content]

Hereinafter, more specific experimental results will be described. (Experiment 1) Using a single crystal manufacturing apparatus as shown in FIG.
KLN single crystal fibers were produced according to the present invention. The temperature inside the furnace was controlled by the upper furnace 1 and the lower furnace 3. The temperature gradient in the vicinity of the single crystal growth part 23 can be controlled by supplying power to the nozzle part 13 and generating heat from the after-heater 12. As a mechanism for pulling down the single crystal fiber, a mechanism for pulling down the single crystal fiber was mounted while controlling the pulling speed uniformly within the range of 2 to 100 mm / hour in the vertical direction. Laser light source 2
As No. 7, a titanium sapphire laser light source, which is a tunable laser whose wavelength can be varied within the range of 780 to 900 nm, was used.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0063

[Correction method] Change

[Correction content]

At the beginning, the powder 1 and the powder 2 are 1: 1.
The mixture was mixed in the ratio of, and put into a crucible. Then, when the peak wavelength fluctuated in the increasing direction, the amount of the powder 1 was increased, and when the peak wavelength fluctuated in the decreasing direction, the amount of the powder 2 was increased.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location C30B 29/62 7202-4G C30B 29/62 E H01S 3/16 H01S 3/16 // G02B 6 / 00 371 G02B 6/00 371

Claims (8)

[Claims] 1. A method for producing an oxide single crystal in which a raw material for an oxide single crystal is supplied into a crucible and melted, and a seed crystal is brought into contact with the melt to grow the oxide single crystal. A laser beam is applied to the oxide single crystal, the output light from the oxide single crystal is measured, and the composition ratio of the raw material supplied to the crucible is controlled according to the measured value. A method for producing an oxide single crystal, comprising: 2. The oxide single crystal is grown while pulling down the melt downward from the crucible, and the laser light is applied to the oxide single crystal pulled down downward. Irradiation is carried out, Claim 1 characterized by the above-mentioned.
A method for producing the oxide single crystal described. 3. The oxide single crystal is an oxide single crystal for a solid-state laser, and the oxide single crystal is irradiated with laser light and the converted light obtained by converting the wavelength of the laser light is detected. The method for producing an oxide single crystal according to claim 1 or 2, characterized in that: 4. The oxide single crystal has a second harmonic generation effect, and the oxide single crystal is irradiated with laser light to detect a second harmonic wave of the laser light. The method for producing an oxide single crystal according to claim 1 or 2. 5. The laser light has a wavelength range including a wavelength corresponding to a desired composition, and the output light from the oxide single crystal is detected by a spectrum analyzer. The method for producing an oxide single crystal according to any one of claims 1 to 4. 6. The oxide, wherein a first laser beam having a wavelength larger than a wavelength corresponding to a target composition and a second laser beam having a wavelength smaller than a wavelength corresponding to a target composition are used. The single crystal is irradiated, and the output light corresponding to the first laser light and the output light corresponding to the second laser light are detected. A method for producing an oxide single crystal according to any one of claims. 7. The dimensions of the cross section of the oxide single crystal are measured by an optical sensor.
The method for producing an oxide single crystal according to claim 1. 8. An apparatus for producing an oxide single crystal, wherein an oxide single crystal raw material is supplied into a crucible and melted, and a seed crystal is brought into contact with the melt to grow the oxide single crystal. A raw material supply device for supplying the raw material to the crucible; a driving device for pulling out the oxide single crystal from the crucible; a laser light source for irradiating the oxide single crystal with laser light; A measuring device for measuring the output light from the oxide single crystal; and a control device for controlling the composition ratio of the raw material supplied to the crucible according to the output from the measuring device. A device for producing an oxide single crystal.